Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Systems that read bar codes (bar code readers) electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. The characters are then typically represented in digital form and utilized as an input to a data processing system for various end-user applications such as point-of-sale processing, inventory control and the like.
Systems that read and decode bar codes employing imaging systems are typically referred to as imaging-based bar code system or bar code scanners. Imaging-based bar code systems typically employ an illumination apparatus to flood a target object with illumination from a light source, wherein the target object reflects the incident illumination back to the imaging-based bar code system. The reflected light is then focused through the imaging lens system onto the pixel array, the target object being within a field of view of the imaging lens system.
The illumination system is designed to direct a pattern of illumination light towards a target object such that the illumination pattern approximately matches the field of view (FV) of the imaging system.
The problem present in the existing illumination systems is that the intensity of illumination is greatest in a central area of the illumination pattern, while the outer or fringe areas of the illumination pattern have reduced illumination intensity, also there are abrupt changes in the illumination intensity at the transitional areas. Compounding this problem of existing illumination systems is the fact that the imaging lens system typically tends to collect and focus a greater portion of reflected light from a central area of the FV onto the pixel array than is collected and focused from the fringe areas FV. The non-uniformity of the illumination pattern combined with non-uniformity of imaging system focusing results in non-uniformity of light intensity across the pixel array. This tends to cause changes or fluctuation of the output analog signal read out from the pixel array and therefore reduces the dynamic range of the imaging system and compromises reader performance.
Accordingly, there is a need for an illumination apparatus for an imaging-based bar code system
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.